The invention relates to an antenna having at least two fed radiating elements as claimed in the precharacterizing clause of claim 1.
As is known, in the case of antennas having at least two fed radiating elements, that is to say having a number of fed radiating elements, it is important to achieve as much decoupling as possible between the different radiating elements. Particularly in the case of dual-polarized radiating elements or arrays, a high level of decoupling is desirable between the radiating elements for one polarization and the radiating elements for the other polarization, which is at right angles to it. Such arrays may comprise, for example, a number of elements in the form of dipoles, slots or planar radiating elements, such as those which are known, for example, from EP 0 685 900 A1 or from the prior publication xe2x80x9cAntennenxe2x80x9d [Antennas], Part 2, Bibliographical Institute in Mannheim/Vienna/Zurich, 1970, pages 47 to 50. This document describes, for example, omnidirectional radiating elements with horizontal polarization in the form of a dipole square or a cruciform dipole, in which coupling exists between the two systems which are physically offset through 90xc2x0.
In order to increase the directionality, such radiating elements are normally arranged in front of a reflector. A disadvantage that has been found in this case is that the intrinsically good decoupling in particular between radiating elements with orthogonal polarizations is made worse by arranging them as an array, in particular due to the influences of the reflector.
appropriate decoupling elements have already been proposed in order to compensate for these disadvantages mentioned above.
The previously published DE 196 27 015 A1 has already proposed that decoupling devices in the form of strips or crosses be arranged between the radiating elements, in which case, particularly when using strips, these strips are arranged along the connecting line of two antenna devices, which are arranged offset with respect to one another, in an antenna array. In contrast to already known solutions relating to this, these strips are not arranged transversely with respect to the connection direction between two antenna arrangements, but parallel to the connecting line between two adjacent antenna devices.
The previously published DE 198 21 223 A1 proposes that passive strip arrangements be used as decoupling elements, which are provided such that they are aligned running centrally between in each case two antenna devices, which are arranged offset like an antenna array, between these antenna devices in the transverse direction with respect to the direction in which the radiating elements are fitted, or else are arranged parallel to the direction in which the radiating elements are fitted, and to the side of said radiating elements at the same time. To this extent, this arrangement corresponds to that already proposed in the previously published U.S. Pat. No. 3,541,559, which likewise proposes that the individual decoupling elements be arranged to the side of the individual antennas, like a frame.
Furthermore, GB 2 171 257 A discloses an antenna array which has a number of dipoles arranged vertically one above the other, with a projecting element in each case being arranged above two dipoles which are arranged one above the other, with the aim of improving the decoupling between the dipoles. This antenna array, which is already known from this document, is, in fact, constructed using stripline technology.
The object of the present invention, in the case of antennas having at least two fed radiating elements, in particular in the case of antenna arrays and at the same time in particular in the case of dual-polarized antenna arrays, is to allow a further improved capability for decoupling between the various radiating elements.
According to the invention, the object is achieved by the features specified in claim 1.
Advantageous refinements of the invention are specified in the dependent claims.
It must be regarded as being extremely surprising that, in complete contrast to all the previously published prior art, it is now proposed that conductive decoupling elements be used, with their main extent direction, that is to say with their longest extent in the propagation direction of the electromagnetic wave and/or with their longest extent, being aligned at right angles to a reflector. In this case, the alignment need not correspond exactly to the propagation direction of the electromagnetic wave, and do not correspond exactly to the perpendicular to the plane of a reflector. All that is necessary according to the invention is for the decoupling elements, which are preferably in the form of rods, to be aligned with a component in the propagation direction of the electromagnetic waves, that is to say in particular running at right angles to the plane of the reflector plate, with at least these components representing a greater value than a component at right angles thereto. If the decoupling elements are configured in the form of rods, this means, in other words, that the angle between the longitudinal extent of the decoupling elements and a perpendicular to the reflector plate plane (that is to say to the propagation direction of the electromagnetic waves) is less than 45xc2x0.
The system according to the inventionxe2x80x94and this is particularly surprisingxe2x80x94has critically significant advantages particularly in the case of dual-polarized antennas, which hence comprise, in particular, at least one cruciform dipole or at least one dipole square. In contrast, the coupling elements which are known from GB 2 171 257 A relate only to a dipole arrangement with one polarization, which are also adjacent.
Thus, according to the invention, two mutually perpendicular polarizations are preferably in each case affected, in which no radiating elements located vertically alongside one another, and which could be decoupled, are provided. A further difference to the prior art is that, in the case of dual-polarized antennas, two separate inputs are used, between which the decoupling (or isolation) must be measurable, while, in the case of the improved decoupling with a deeper arrangement with only one polarization, such decoupling is not measurable (as, in fact, there is only one input).
As mentioned, the decoupling elements according to the invention are preferably in the form of rods and/or pins.
The decoupling elements according to the invention can in this case be arranged, for example, between two radiating elements, for example between two or more vertically polarized or horizontally polarized radiating elements, in each case in the region of the connecting line between these radiating elements.
In the case of cruciform dipoles, for example, the decoupling elements according to the invention, which are preferably seated perpendicular on the reflector plate, can be arranged in the immediate area between the individual dipole halves, for example, in plan view, on an angle bisector of a cruciform dipole arrangement.
One or more of the decoupling elements according to the invention can likewise, for example in the case of a dipole square, be arranged within the dipole square, and in this case once again preferably on an angle bisector of the dipole square.
The decoupling elements, which are in the form of rods according to the invention, extend as stated with their greatest longitudinal extent or component in the propagation direction of the magnetic waves and/or at right angles to the reflector plane. In this case, the decoupling elements may have a uniform cross section or widely differing cross-sectional shapes, for example with a round cross section or with a regular cross section or an irregular n-polygonal, for example square or hexagonal cross section, etc.
However, the cross section may in this case also vary over the length of the decoupling elements according to the invention. It is likewise possible for the cross-sectional areas not to be rotationally symmetrical but, for example, to have different longitudinal extents along two mutually perpendicular section axes running parallel to the reflector surface.
Finally, it is also possible for the decoupling elements according to the invention also to be provided, in particular at their end opposite the reflector plate, with formed-out regions or fixtures, which may also extend transversely with respect to the vertical extent component of the decoupling element, and hence transversely with respect to the propagation direction of the electromagnetic waves and/or parallel to the plane of the reflector plate.